feat: Phase 9 — developer experience, extensibility, and community growth

New crates:
- quicproquo-bot: Bot SDK with polling API + JSON pipe mode
- quicproquo-kt: Key Transparency Merkle log (RFC 9162 subset)
- quicproquo-plugin-api: no_std C-compatible plugin vtable API
- quicproquo-gen: scaffolding tool (qpq-gen plugin/bot/rpc/hook)

Server features:
- ServerHooks trait wired into all RPC handlers (enqueue, fetch, auth,
  channel, registration) with plugin rejection support
- Dynamic plugin loader (libloading) with --plugin-dir config
- Delivery proof canary tokens (Ed25519 server signatures on enqueue)
- Key Transparency Merkle log with inclusion proofs on resolveUser

Core library:
- Safety numbers (60-digit HMAC-SHA256 key verification codes)
- Verifiable transcript archive (CBOR + ChaCha20-Poly1305 + hash chain)
- Delivery proof verification utility
- Criterion benchmarks (hybrid KEM, MLS, identity, sealed sender, padding)

Client:
- /verify REPL command for out-of-band key verification
- Full-screen TUI via Ratatui (feature-gated --features tui)
- qpq export / qpq export-verify CLI subcommands
- KT inclusion proof verification on user resolution

Also: ROADMAP Phase 9 added, bot SDK docs, server hooks docs,
crate-responsibilities updated, example plugins (rate_limit, logging).

crates/quicproquo-server/Cargo.toml

@@ -10,8 +10,13 @@ name = "qpq-server"
 path = "src/main.rs"
 
 [dependencies]
-quicproquo-core  = { path = "../quicproquo-core" }
-quicproquo-proto = { path = "../quicproquo-proto" }
+quicproquo-core       = { path = "../quicproquo-core" }
+quicproquo-proto      = { path = "../quicproquo-proto" }
+quicproquo-plugin-api = { path = "../quicproquo-plugin-api" }
+quicproquo-kt         = { path = "../quicproquo-kt" }
+
+# Dynamic plugin loading
+libloading = "0.8"
 
 # Serialisation + RPC
 capnp         = { workspace = true }